It is well known that, when tubular plastic film is extruded in a molten state from an annular die and then passed as an air filled bubble before being flattened by passing through a collapsing frame and between a pair of nip rollers, irregularities occur in the thickness, i.e. gauge, of the film. Since the flattened film is then usually wound on a storage roll, it is usually necessary to provide apparatus for moving the two layers of the flattened film relatively to one another so that irregularities in film thickness, i.e. in its gauge, are distributed across the width of the storage roll to avoid the problems which would arise if this was not done. This process is commonly known as gauge distribution, and various types of apparatus are used for this purpose. One type of gauge distribution apparatus is described in U.S. Pat. No. 4,676,728 (Planeta) issued Jun. 30, 1987, and another type is described in U.S. Pat. No. 5,589,201 (Tkach et al) issued Dec. 31, 1996, the contents of these patents being incorporated herein by reference.
In the patents mentioned above, gauge distribution is effected by passing a tubular flattened film around at least one turning bar whose position with respect to the film is varied. In the preferred embodiment described in the earlier patent, the turning bars are vertical or inclined to the vertical whereas, in the described embodiments in the later patent, the turning bars are horizontal. It has been found in practice that for various reasons such as imperfect alignment, film sliding and non-uniform circular cross-section of the bubble, the flattened film passing from the gauge distribution apparatus to the storage roll tends to wander laterally from its desired path. Attempts have been made to overcome this problem by placing edge guides which guide the flattened film in the desired path to the storage roll, but such edge guides tend to induce tension in the flattened film which creates non-uniformity on the edges of a roll of flattened film on a storage roll.